Introduction

Only less than 3% of the water resources of the Earth are freshwaters, and only one-hundredths of a percent of these is adapted to human consumption. Due to the rapid and disorganized growth of population, careless management, and excessive consumption in agricultural and industrial activities, these valuable resources are facing a serious crisis [1,2,3,4]. Groundwater is at risk of exposure to heavy metals (HMs) from different sources, including agricultural runoffs as well as urban and industrial wastewaters [5, 6]. HMs are stable contaminants which, unlike their compounds, are not degraded in nature through biological processes [7,8,9]. They are among the highest priority pollutants based on the 2007 CERCLA Priority List of Hazardous Substances [10].

Arsenic (As) is the most common cause of acute heavy metal poisoning in adults. Long-time exposure to arsenic can cause malignant melanoma, hyperkeratosis, cardiovascular diseases, peripheral nervous system problems, and cancer. The American Environmental Protection Agency (EPA) and the World Health Organization (WHO) recommended the permissible limits for arsenic in drinking water to be 50 μg/L and 10 μg/L, respectively [11,12,13]. Chromium (Cr) is also an element which a high concentration in food resources and drinking water. This metal is very harmful to human health, seriously damaging lungs and kidneys. WHO and USEPA have stated 10 and 15 μg/L, respectively, as allowable limits of Cr in drinking water [14, 15]. Moreover, lead (Pb) is a metal with highly toxic and carcinogenic effects for humans. Exposure to high concentrations of Pb causes complicated health problems, such as behavioral disorders, dementia, and reduced ability to learn [12, 16]. In addition, copper (Cu) at very high levels is toxic and can cause vomiting, diarrhea, loss of strength, and cirrhosis of the liver. Water turns blue-green in color as the corroded copper comes off the inside of pipes and appears in the water as a precipitate [2, 17]. Iron (Fe) is another heavy metal of concern, particularly because ingesting dietary Fe supplements may acutely poison young children. Ingestion accounts for most toxic effects of Fe because iron is absorbed rapidly in the gastrointestinal tract. It can cause a metallic taste in drinking water, and exposure to high concentrations of Fe exerts adverse effects on target organs, such as liver, the cardiovascular system, and kidneys [18].

Today, health risk assessment is an important method to assess potential negative outcomes for people exposed to a risk factor [19, 20]. In this regard, recognizing HM contaminations and their possible sources is an issue which requires investigation. Thus, several risk assessment studies were conducted in several countries on consumers’ exposure to HMs. In Saudi Arabia, for instance, Zabin reported that heavy metals such as Cu, manganese (Mn), zinc (Zn), and Fe [21] have entered water sources from waste leachate and landfill sites. In Iran, the effects of Zn, Pb, cadmium (Cd), Cr, and Cu were investigated [22, 23] and in China, the concentrations of mercury (Hg), Pb, Cd, Zn, and Cu in foods consumed in industrial regions were assessed [24]. In Italy, numerous studies have evaluated the risk of heavy metal exposure through diet in people [2, 9, 25,26,27] and similar studies have been conducted on HM toxicity in animals [28, 29]. Ni et al. assessed the health risk of Cr and As in two lakes used as drinking water supplies of the surrounding regions, suggesting a significant risk of HMs threatening the people residing in the region [30]. The information obtained from risk assessment serves as an important instrument for helping authorities and decision-makers in environmental and sanitary risk management and communication [31].

Neyshabur Plain is located in the center of Razavi Khorasan Province, North-East Iran. In this geographical area, no research about HM contamination in drinking water and its potential effects on human health has so far been conducted. The major reasons motivating the present study in this area were the geological nature of the plain, presence of several active mines, chemical quality of water, and corrosion potential of water resources which can lead to the release of heavy metals into water supply systems. This study aimed to assess HMs levels in the drinking water of Neyshabur Plain to assess the related risk of adverse effects on consumers.

Materials and Methods

The Studied Area and Sampling

The studied area, Neyshabur Plain, is located in the center of Ravazi Khorasan Province, Iran, and is one of the sub-basins of the Central Plain area. This region is located at the longitude of 58° 13′ to 59° 30′ and latitude of 35° 40′ to 36° 39′ (Fig. 1). The mean temperature in this region is 12 °C and the annual precipitation for the entire area is reported to be 278 mm on average (The mean annual precipitation in the area’s plain and altitudes has been estimated to be 243 and 326 mm, respectively). Totally, 158 drinking water samples were collected from the wells, springs, and distribution system network of the area during two high-precipitation and low-precipitation seasons from Neyshabur Plain (Neyshabur, Chakaneh, Ghadamgah, Bar, Kharv, Eshghabad, and Darood) in 2016. The sites of sampling are illustrated in Fig. 1. The samples were collected in separate polyethylene bottles for measurement of selected heavy metal (Fe, Cu, Zn, Pb, As, and Cr). Approximately 2 mL of 65% HNO3 was added to prevent metal precipitation. The coordinates of the sampling site as well as the date and hour of sampling were recorded by GPS.

Fig. 1
figure 1

Map of the study area and sampling sites

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Method

HMs Analysis

A digestion solution for tissue was prepared with 6 mL of 65% nitric acid (HNO3) (Carlo Erba) and 2 mL of 30% peroxide hydrogen (H2O2-Carlo Erba) over a 50-min operation cycle at 200 °C. After mineralization, the vessels were opened if a temperature < 25 °C was reached, and then the content was decanted in falcon tubes and ultra-pure water (Merck) was added to the samples up to 30 mL. To quantify metals, an ICP-MS Elan-DRC-e (Perkin–Elmer, USA) was utilized. Analytical blanks were processed in the same way as the samples, and concentrations were determined using standard solutions prepared in the same acid matrix. Standards for instrument calibration were prepared with a multi-elements certified reference solution ICP Standard (Merck). The method detection limits (MDLs) estimated with 3r of the procedure blanks were (mg/kg w. w.): As 0.013, Cd 0.002, Cr 0.003, Pb 0.001, Hg 0.025, Mn 0.005, Ni 0.007, V 0.025, Se 0.03, and Zn 0.009, respectively. For each batch of mineralization, a laboratory-fortified matrix (LFM) was processed for quality control and recovery rates were obtained between 91.5 and 110%. Measurement of HMs was performed using an ICP device, OES model, Spector ARCOS, Germany. The method presents the factor of concentration in the samples by an inductively coupled plasma emission spectrometer device (ICP-OES), Spector ARCOS, Germany. The sampling method, preservation of samples, and experiments were performed according to the book Standard Methods for Water and Wastewater Experiments [32]. The experiments were performed in Ferdowsi Mashhad Laboratory. To measure the accuracy of the atomic absorption device (Spector ARCOS, Germany), the standard sample and unknown samples were experimented in triplicate, where the accuracy ranged between 90 and 95% on average.

Pollution Evaluation Indices

After monitoring the level of heavy metals, water quality pollution indices were calculated. Heavy metal pollution index (HPI) and heavy metal evaluation index (HEI) were employed to evaluate drinking water quality [33,34,35].

HPI

The heavy metal pollution index is expressed by Eqs. (1) and (2) as follows:

$$ HPI=\frac{\sum \limits_{i=1}^n{w}_i Qi}{\sum \limits_{i=1}^n{w}_i}. $$
(1)
$$ Qi=\sum \limits_{i=1}^n\frac{Mi\left(-\right) Ii}{Si- Ii}n100 $$
(2)

where Qi and Wi are the sub-index of the parameter and the unit weight of the ith parameter, respectively; n is the number of parameters considered; Mi, Ii, and Si are the monitored values of heavy metals and ideal and standard values of the ith parameter, respectively; and sign (−) indicates the numerical differences between the two values, ignoring the algebraic sign. An HPI index less than 100 indicates that it is a low-level heavy metal and has no adverse health effects. When the value of HPI is equal to 100, it indicates that the threshold risk and adverse health effects are possible. If HPI is more than 100, water cannot be used for drinking and is unsuitable for consumption.

HEI

HEI demonstrates the overall quality of water with respect to heavy metals, calculated based on Eq. (3), where Hc and Hmac are the monitored value and maximum admissible concentration (MAC) of the ith parameter, respectively.

$$ HEI=\sum \limits_{i=1}^n\frac{Hc}{Hmac} $$
(3)

The applied parameters and constants for the calculation of HPI and HPI (according to WHO guidelines) are presented in Table 1. The classifications of the HEI index is as follows: low (less than 10), medium (between 10 and 20), and high (more than 20) [36, 37]. Parameters used for HPI and HEI indices in drinking water are given in Table 1.

Table 1 Parameters and constants used for the calculation of HPI and HPI (according to WHO guidelines)
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HMs Health Risk Assessment

Toxic compounds are categorized into carcinogenic and non-carcinogenic metals. Accordingly, in health risk assessment resulting from stressor factors, carcinogenicity and non-carcinogenicity of the risks are of interest, each following the mathematical relations below according to the standard instructions of EPA and WHO:

Chronic daily intake (CDI) [32]

CDI = C × DI/BW where C is the metal concentration in terms of mg/L, DI represents the rate of daily intake in consumption in terms of L/day (2.36 L/d according to the daily consumption of drinking water), and BW is the mean weight of adults in terms of kg (72 kg). The ratio of the non-carcinogenicity potential risk has been calculated by the following Eq. (4):

Footnote 1PHQ = CDI/RfD

According to the database of American EPA

Reference dosage of non-carcinogens, D jrf (mg/kg/day)

8E-01, 5.0E-03, 3.0E-01, 1.4E-03 mg/kg/day for Fe, Cu, Zn, Pb [33].

In order to investigate the carcinogenicity risk of As and Cr, the following relation was used:

Footnote 2Rc = CDI × SF

Moreover, the total risk out of the sum of carcinogenicity and non-carcinogenicity risks was calculated for each station [30]: The chronic daily consumption rate (CDI) and SF factor of As contamination slope (in terms of mg/kg per day) is 1.5 according to the instruction of American EPA and 4.1 mg/kg/day for Cr.

Statistical Analysis

In this study, the map of wells and stations was prepared using the Arc GIS V. 10.3 software. Furthermore, the map of the distribution of the studied HMs was plotted in the studied range and then the rasterized map of risk was generated based on the total risk value. This rasterized map can be classified into different groups, demonstrating the potential risk changes in the region. In addition, using Excel 14.0 (Microsoft, Redmond, WA, USA), the mean, range of d changes, and standard deviation of the data were calculated. For a statistical examination of the data, Minitab statistical software version 15 (Minitab Inc., State College, PA, USA) was employed.

Results and Discussion

Table 2 summarizes the HM concentrations in groundwater samples collected from Neyshabur Plain sites (Fig. 1). The Pb concentrations in drinking water samples ranged from 1.96 to 3.51, 1.97–2.95, 2.28–3.31, 2.43–4.24, 1–4, 10–12, and 1–4 μg/L, in Neyshabur, Bar, Chakaneh, Kharv, Darood, Eshghabad, and Ghadamgah sites, respectively (Table 2). It was shown that lead concentration in all of the studied water samples was within the standard guidelines of 0.01 mg/L set by WHO [38]. The highest Pb concentration was observed in the groundwater water sample (12 μg/L) collected from Eshghabad. Studies report that chronic exposure to lead can cause anemia and high blood pressure, especially in the elderly and middle-aged groups. However, water with less than 0.05 mg/L concentration of Pb may have a slight risk of behavioral changes and the possibility of neurological impairment in young children with developing brain tissues [39]. The mean concentration belonged to Fe in a drinking water sample, ranging from 1.30 to 29.7 μg/L for Neyshabur and Ghadamgah throughout the study area, respectively. This value was beyond the recommended concentration of < 0.1 and 0.3 mg/L set by the WHO [38]. The presence of iron higher than 0.3 mg/L in water causes adverse esthetic and health effects when ingested by the residents around Neyshabur City. The high concentration of Fe in Neyshabur groundwater wells may be due to the leaching of Fe from sewer pipes and other non-point sources such as storm runoff and metal disposal. Nitrate leaching in groundwater, oxidation, and a decrease in pH may lead to the dissolution of iron, thus increasing Fe concentration in groundwater [40]. Cr concentration in the studied water samples ranged from < 0.003 to 20 μg/L for Neyshabur City and Ghadamgah throughout the study area, respectively. The samples taken from Neyshabur Plain were within the WHO recommended water quality guidelines of < 0.05 mg/L [38]. The high Cr concentration in Neyshabur City drinking water sample may be the result of the high infiltration of water and leachates from landfill and dumpsites due to heavy rainfall [41]. Results indicated that maximum and minimum contents of As (ppb) in the groundwater sample were 9.86 to < 0.013 respectively. The maximum and minimum detection values of Zn, i.e., < 0.009 and 11.01 μg/L, were recorded in Chakaneh and Neyshabur City, respectively. In the study area, all drinking water samples were within the WHO recommended standard limits of < 5.0 and < 3.0 mg/L for Zn [38]. Studies conducted by Mirzabeygi on the heavy metal contamination and health risk assessment of the drinking water of Sistan and Baluchistan Province, Southeastern Iran, showed the maximum Cr and Cd concentrations, i.e., 79.3 μg/L and 20 μg/L, were observed in Iranshahr and Nikshahr area, respectively, which can be attributed to the chromite mines and bedrocks hosting chromite deposits in Iranshahr area. Also, the highest Pb concentration was found in the groundwater water sample (80 μg/L) collected from Saravan [42]. Edokpayi et al. conducted a study on water quality assessment and human risk assessment due to heavy metals in groundwater around the Muledane area of Vhembe District, Limpopo Province, South Africa, and reported that Cr and Fe concentrations were in the range of 0.005–0.15 and 0.15–1.86 mg/L for B1–B8 throughout the study area, respectively. Results also revealed that the concentrations of Pb and Cd ranged from 0.002 to 0.026 and 0.003 to 0.24 mg/L in water samples throughout the study region, respectively [43]. Therefore, the findings of this report are in line with our results. Results also showed that no HM concentration exceeded the standard concentration recommended by WHO for HMs in drinking water resources. Considering the toxicity of some elements as well as their bioaccumulation and long-term effects on consumers, a frequent monitoring of HM concentration in water resources and their relative risk is inevitable.

Table 2 HM concentrations (μg/L) in water samples collected from the study area
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Pollution Evaluation Indices of Water

The results of HPI and HEI are presented in Table 3. The HPI and HEI values ranged from 47.7 to 58.8 and 1.76 to 7.58, respectively. Based on the results, the HPI index in all the samples was less than 100, indicating that it is a low-level heavy metal. Moreover, the HEI values ranged from 1.76 to 7.58. The proposed HEI criteria are as follows: low (HEI < 10), medium (HEI = 10–20), and high (HEI > 20). Based on this research, the HEI index in all stations belonged to the low category. The results reported by Boateng et al. demonstrated that HPI index in all the samples is above the critical limit (HPI > 100) and the HEI value in 10% of the studied region is > 20.Moreover, 58 and 32% of samples were within low and medium zones, respectively [44].

Table 3 Mean HPI and HEI of groundwater at each station for heavy metals
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Ghaderpoori et al. performed a heavy metal analysis and quality assessment on the drinking water of Khorramabad, Iran. Results showed that HPI value is all samples is less than 100 and, therefore, the drinking water quality is good in terms of heavy metals [22]. The results were similar to those of our study.

CDI

Based on the method proposed in the previous section, the results of CDI intake can be observed in Table 4. The maximum daily consumption rate belonged to Fe in the drinking water of Neyshabur City (0.683 × 10−8 mg/kg/day). The order Fe > Zn > Cu > Cr > Pb > As was observed between the mean daily consumption rate of the elements across the selected wells.

Table 4 Chronic daily intake of studied HMs (mg kg/day)
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Human Health Risk Assessment (HQ)

Today, health risk assessment is one of the best approaches for investigating the potential risk of exposure to HMs for humans, offering very important information for public health decision-makers to protect the health of consumers. In examining the non-carcinogenicity and carcinogenicity risk of Fe, Cu, Zn, Pb, As, and Cr in groundwater resources of Neyshabur Plain, results revealed that the carcinogenicity risk of As and Cr varied within 0.02× 10−7–10.64× 10−7 a year, suggesting that no significant carcinogenicity risk jeopardizes the people living in the region. Also, in examining the non-carcinogenicity risk which lay within 40.15× 10−7 to 136.32× 10−7, it was shown that 40–136 persons are at risk of exposure to non-carcinogenicity of metals per every 10 million inhabitants (Table 5). Furthermore, based on the results, the risk of non-carcinogenic elements (HQ) showed a far greater value than the elements with carcinogenicity risk. The total risk in the studied elements varied from 40.164× 10−7 to 174.8× 10−7. In this study, the maximum mean risk was related to Pb and Cu with the respective values of 60.10× 10−7 and 33.99× 10−7 (Table 5). To better observe the results of risk resulting from the metals, in addition to the risk resulting from heavy metals in the water resources of Neyshabur Plain, the stations of Bar, Chakaneh, Kharv, Darroud, Eshghabad, and Ghadamgah were also investigated and the results obtained were reported (Figs. 2 and 3). In a comparison of the potential risk of heavy metals for Neyshabur City and its surroundings, it is evident from Fig. 2 that the maximum and minimum total risks belonged to Chakaneh and Bar stations with the respective values of 122.5 × 10−7 and 106.78 × 10−7. Overall, in terms of risk, the studied area lies within a tolerable range as specified by the American EPA regarding the HM content in drinking water [45]. In other words, the central and Northeastern parts of the city are more exposed to the potential risk of HMs, while the Western parts are less exposed. Overall, based on the investigations, it was found that, due to the presence of mines and hybrid cycle plants in the Northeastern part of the region as well as the wastewaters produced across the city in the central part, the probability of entrance of some elements into water resources exists, which can elevate the concentration of elements with an increased risk in these regions. In a study conducted by Sakizadeh and Mirzaei, the Fe, Mn, Cu, and Cr health risk assessment in drinking water of some wells and springs of Shush and Andimeshk, Iran, was performed. Results showed that, except for iron, mean heavy metal concentrations were higher than the standard levels [46]. A study on the assessment of contamination and health risk of heavy metals in selected water bodies around gold mining areas in Ghana in 2018 reported that the concentration of Al, Fe, and Mn, in water samples exceeded the contamination levels with reference to the WHO and USEPA guideline limits. The results also revealed that arsenic has a CR value higher than the acceptable limit (1.8 E-02) in the mining sites, posting a carcinogenic health threat [47]. In the research conducted by Khan [48] regarding the risk assessment of HMs in groundwater resources of Savat regions in the Northern part of Pakistan, it was found that the ratio of the risk of all studied heavy metals, including Mn > Cr > Cu, was less than 1. Therefore, the data of this research are in line with our results. Moreover, Shizhen Zhang [49] reported that the risk of carcinogenic elements were within the range of 1.05 × 10−5 and 3.5 × 10−4, above the standard level recommended by the EPA. Meanwhile, the carcinogenicity risk of Cr was greater than that of other elements (99.66%). The risk of the values of non-carcinogenic elements across all of the measured elements is less than the standard recommended by the EPA, and Cr had the greatest contribution, accounting for 36% of the total risk of the non-carcinogenic elements. The results of this research indicate that greater attention should be paid to the health risks resulting from Cr in ground waters. These findings, i.e., Cr being the element with the maximum risk, are not in line with those of our study in which Pb claimed this position. In a study by Fallahzadeh et al. on the spatial analysis and health risk assessment of heavy metal concentrations in drinking water resources, it was found that iron and zinc had the highest concentrations, respectively, in the entire studied area. This research also reported that the average lifetime cancer risks for lead in Ardakan and nickel in Meibod and Bahabad were 1.09 × 10−3, 1.67 × 10–1, and 2 × 10−1, respectively [50]. In addition, the study conducted by Zhang et al. on heavy metal pollution of drinking water sources in the Liujiang River Basin and related health risk assessments reported the average non-carcinogenic health risks to be between 3.53 E-12 and 2.87 E-09 a–1 values lower than the maximum allowance levels recommended by EPA. Also, carcinogens Cr and As were the main causes of health risks in the aquatic environment of the Liujiang River Basin [51]. In another study conducted in Turkey on metals soluble in groundwater and surface water resources, the results suggested that the hazard quotient (HQ) of the carcinogenicity risk of metals is greater in groundwater resources than in surface water resources, as this index equaled 7, 2.6, and 1 for As, Mg, and Zn, respectively. However, this index was below 1 for the metals of interest. These results show that even the basins without contamination can threaten human health. Therefore, the potential carcinogenicity risks should be further inspected in these regions [52]. Li assessed the trace elements in the terminal tap water of Hunan Province, South China, and its potential health risks. Results indicated that 10% of the water samples were above the level of Cd guideline by WHO, i.e, .003 mg L−1. Moreover, 3% of the samples had a Fe level and 1% had an As level above the WHO limits of 0.3 and 0.01 mg L−1, respectively. Moreover, the individual and total HQ values in the noted study were both less than 1 [53].This research suggested that no health risk threatened the population of interest during the course of the study in terms of HMs. According to the instruction of the American EPA, the acceptable health risk of metals in a year is 10−4–10−6. Nevertheless, considering the difference in the effect of metals across different consumers in terms of sex or age, this investigation should be performed especially for elements that are important in water quality (e.g., Co and Hg).

Table 5 Hazard Quotient (HQ) and Potential carcinogenic risk of HMs in drinking water in 44-70 years old (×10-7)
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Fig. 2
figure 2

Potential carcinogenic risk in the drinking water of Neyshbur Plain (10‑7)

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Fig. 3
figure 3

Non-Carcinogenic potential risk of HMs via drinking water in the drinking water of Neyshbur Plain (10–7)

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Conclusion

In this research, the heavy metal and pollution evaluation indices (HPI and HEI) were first calculated, and then a health risk assessment (HQ) was performed to assess the carcinogenic and non-carcinogenic risks of heavy metals in groundwater wells in the Neyshabur Plain for consumers (44–70 years old).

The findings of the present research are summarized as follows:

  1. 1.

    The highest average value in water samples analyzed in the groundwater of the studied area was observed for iron (9.78 ± 5.61 μg/L) and the lowest belonged to arsenic (1.30 ± 2.99 μg/L), but both values were well below the limits recommended by the WHO and the Iranian national standard.

  2. 2.

    The HPI index in all the samples was less than 100, showing that it is a low-level heavy metal. Therefore, the drinking water quality is good in terms of heavy metals.

  3. 3.

    The human health risk assessment demonstrated the HQ values to be < 1, suggesting an acceptable level of non-carcinogenic adverse risk.

  4. 4.

    The maximum mean of risk belonged to lead and copper with the respective values of 60.10 × 10−7and 33.99 × 10−7 from the selected wells. Considering the standard limit defined by USEPA for the acceptable range of risk (10-4–10-6), the studied wells did not show any value above the allowable limit for the noted elements.

  5. 5.

    The HQ values for consumer groups (44–70 years old) were lower than the recommended limit values (< 1), but it cannot be concluded that potential non-carcinogenicity risks are non-existent since possible exposure to heavy metals via food and skin may also pose a risk.